Oil drag loss in oil-flooded, twin-screw compressors Abdan, Suraj; Stosic, Nikola; Kovacevic, Ahmed ...
Proceedings of the Institution of Mechanical Engineers. Part E, Journal of process mechanical engineering,
08/2023, Volume:
237, Issue:
4
Journal Article
Peer reviewed
Open access
Rotary twin screw compressors are widely used because of their high efficiency and reliability. Their most common mode of operation is as oil-flooded machines when delivering air and gases at ...moderate pressures and flow rates. In order to achieve the best performance, it is essential to be able to predict the optimum amount of oil, required for the oil injection process, accurately. Analytical procedures for the design and performance estimation of twin screw compressors are well developed and widely available, but the determination of oil drag losses, in oil-flooded machines is only guesstimated. This paper describes a more detailed and accurate procedure for estimating oil drag loss, using a combined Couette-Poiseuille flow model and gives the results of studies on three sizes of machines operating over a range of pressure ratios and speeds. To this end, a parametric analysis has been developed based on a combined Couette-Poiseuille flow model and has been used to estimate the individual effects of pressure ratio, the various clearances and the oil viscosity on the total drag loss, for different sizes of the compressor. It can be seen from the results that at pressure ratios of up to 8.5, the drag loss due to the discharge axial clearance gap is nearly 2/3rd of the total, while nearly 1/3rd is due to the radial clearance. At normal operating speeds, the loss due to the interlobe clearance is insignificant, but as the pressure ratio increases, this rises more rapidly than that due to the axial and radial losses. The gain in the drag loss due to greater oil viscosity becomes more significant as the compressor size is increased. In larger machines, when clearance values are increased, the radial and axial elements of the drag loss are reduced more rapidly than that due to the interlobe loss.
Abstract
Computational Fluid Dynamics (CFD) as a predictive tool is playing an increasing role in the design and optimization process at Compressors and Vacuum Pumps Systems (CVS) Engineering GmbH. ...Design optimization using Design of Experiment (DoE) and continuous improvement of our products has led to an increase in the use of CFD and other predictive tools. This paper investigates the use of CFD combined with Conjugate Heat Transfer (CHT) to optimize the flow and the cooling inside a rotary screw compressor.
The adiabatic and volumetric efficiencies are key performance parameters of any positive displacement machines including twin screw compressors. These efficiencies are affected by clearances and ...leakages in these machines. The leakage happen because of clearance gap and pressure difference between two pressurized chambers the compression module. In this work, findings from all the numerical and mathematical models are presented for different leakages in the twin-screw compressor. Authors proposed an iterative method to estimate the leakages by taking in account the geometry of the clearance, friction and local resistances. An experimental set up to collaborate the leakage model is presented, which can be used for further investigation of these leakages.
Energy costs are typically the largest cost element in the life-cycle of a compressed-air system (CAS). Real-time usage information as well as historical data can help identify whether the CAS is ...functioning properly. To this end, modern variable-speed drives are able to provide this information as well as produce soft-sensor estimates of volume flow rate production and specific energy consumption of a CAS. In this paper, an identification (ID) run sequence for a twin rotary screw compressor-operated system is proposed to identify the total system volume, to improve the estimation accuracy of a volume flow rate soft sensor, and to create a specific energy consumption map for the CAS performance monitoring. Laboratory measurements are carried out to evaluate the feasibility of the proposed ID run and related estimations. Moreover, possible usage applications of the proposed methods are discussed.
Constant torque motors are needed for rotary screw compressors that are used for cooling and other applications. In such systems, the torque demanded by the load is approximately the same over the ...whole range of mechanical speeds. In this paper, the use of multi-phase induction machines is investigated for this type of application. The requirement of low stator current distortion is considered. A scheduled approach is used to provide the best possible tuning for each operating point, similar to the concept of gain scheduling control. Simulations and laboratory tests are used to assess the proposal and compare it with finite-state predictive control. The experiments show that a trade-off situation appears between the ripple content in stator currents in the torque-producing and harmonic planes. As a consequence, the controller tuning appears as an important step. The proposed method considers various figures of merit with cost function tuning, resulting in a scheduled scheme that provides improved results. It is shown that the approach leads to a reduction in current ripple, which is advantageous for this particular application.
Screw compressors, as rotary machinery, are capable of working with high compression ratios for gas compression. They transform the mechanical work done by an electric motor or turbine into the ...potential energy of a gas, by reducing its volume and increasing the pressure. The essential elements of these compressors are the two helical rotors with lobes, mounted in a housing. Existing rotors in the construction of compressors are working bodies whose composite profiles include circle arcs, line segments and cycloidal curves, while also often including non-analytical curves. Such geometry of profiles gives the gear processes superior characteristics, in the sense of reducing friction and improving sealing conditions. This paper analyses, by analytical approach, the possibility of constructing a multilobated conical screw compressor with a number of lobes Z, Z + 1, of the male and female rotor. The parametric equations of the contained worm and the kinematics of the working process of the conical screw compressor shall be defined. The theory of surface wrapping comprises analytical methods of study, which were developed on the basis of the fundamental theorems on wrapping of known surfaces in differential geometry and the kinematics laws on rotor movements. Thus, this paper proposes an algorithm based on the approach to the problems analyzed under the "virtual focal points theorem" between the complex surfaces of the conical surface lobes, which constitute the active lobes of the male and female rotors. Normal to active surfaces are defined, and also the speed in relative movement, in the "gear" process of the conical screw compressor. Regarding rotors in conical screw compressors, the circular pitch of the teeth is constant. Also, the screw pitch of the conical compressor rotors is a constant value. In these conditions, the rotors of the screw compressors are acknowledged as active surfaces, conical screw surfaces with constant axial screw pitch. The cross section (in the normal plane to the driving rotor axis) determines a plane gear. This defines the specific winding condition, and the shape of the conical screw surface of the female rotor.
The actives surfaces of screw compressors are helical surfaces, cylindrical and uniform pitch. The generation of helical surfaces can be done using tools bordered by revolution surfaces (as end mill ...cutter, or disk cutter). The shaping of generating tools is based on fundamentals theorem of the enveloping surfaces. This paper consists to propose a graphic solution, using specific tools of the design environment AUTOCAD, to problem concerning the shaping end mill tool which generates the helical flute of male rotor component of screw compressor. The algorithm has been developed based on a complementary theorem - "The theorem of substituting circles family".
Rotary twin screw machines are used in the wide range of industrial applications and are capable of handling single and multiphase fluids as compressors, expanders and pumps. Concentration of liquid ...in the inlet flow can influence the performance of the machine significantly. Characteristics of the multiphase flow at the suction of a screw compressor depend on the local flow velocities and concentration. Local flow velocity measurements inside the screw compressors are difficult to obtain. However other flow properties such as local pressures are easier to attain. It is therefore useful to carry out experiments with local pressure variations in the suction which can be used to validate the 3D numerical Computational Fluid Dynamic (CFD) models that could help in studying the single and multiphase flow behaviour in screw compressors. This paper presents experimental efforts to measure the local pressure losses inside the suction plenum of the screw compressor. Pressure variations are measured at 23 locations in the suction port at various operating conditions and compared with 3D CFD model. The grid generator SCORGTM was used for generating numerical mesh of rotors. The flow calculations were carried out using commercial 3D solver ANSYS CFX. It was found that the local pressure changes predicted by the CFD model are in the good agreement with measured pressures. This validated the use of CFD for modelling of the single phase flows in suction of screw machines.
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